Before installing the 64-bit flash player you need to check if there already is a plugins folder in your .mozilla folder. Click on your Home Folder launcher and press Ctrl+H (this will make your hidden folders visible) and open the .mozilla folder and look for a folder called plugins. If the folder isn’t there you need to make it first, open a terminal window (press Ctrl+Alt+T) and copy+paste the following line:

sudo mkdir -p .mozilla/plugins

To unpack and move the downloaded file into your .mozilla/plugins folder copy+paste the following lines into your terminal window: